1. Technical Field
The present invention relates to an actuator device that includes a piezoelectric element formed of a lower electrode film, a piezoelectric layer made of a piezoelectric material, and an upper electrode film, all of which are formed on a vibration plate. The invention also relates to a liquid-jet head using the actuator device, and to a method of manufacturing the actuator device.
2. Related Art
An actuator device mounted, for example, on a liquid-jet head that ejects liquid droplets, has a piezoelectric element, which produces a displacement when a voltage is applied. A well-known example of such a liquid-jet head is a type of ink-jet recording head. The type of ink-jet recording head ejects ink droplets from a nozzle orifice communicated with a pressure generating chamber, a part of which is formed by a vibration plate. A deformation of this vibration plate caused by the piezoelectric element pressurizes the ink in the pressure generating chamber, and thus the ink droplets are ejected. The type of ink-jet recording head has two types that have been already put into practical use. One is equipped with a longitudinal-vibration-mode piezoelectric actuator device that extends and contracts in the axial direction of the piezoelectric element. The other is equipped with a flexure-vibration-mode piezoelectric actuator device.
In the former, that is, the ink-jet recording head equipped with a longitudinal-vibration-mode piezoelectric actuator device, the volume of the pressure generating chamber can be changed by a contact of just an end face of the piezoelectric element with the vibration plate. As a consequence, a head suitable for a high-density printing can be manufactured. This one, however, has some problems. The piezoelectric element has to be cut into a comb shape in accordance with the pitch at which the nozzle orifices are arranged, but this is a difficult process. The cut pieces of piezoelectric element have to be positioned at, and fixed to, the pressure generation chambers. This operation makes the manufacturing process complicated. In contrast, in the latter, that is, the ink-jet recording head equipped with flexure-vibration-mode piezoelectric actuator device, the piezoelectric element can be made to be attached to the vibration plate in a relatively easy process. Specifically, the attaching can be done by applying, and then by baking, a green sheet of a piezoelectric material to the pressure generating chambers in accordance with the shape of the pressure generating chambers. This one, however, has its own problems. The use of flexure vibration requires a space of a certain degree of large area, and makes a high-density arrangement difficult. In this respect, an actuator device is developed to solve the inconvenience of the ink-jet recording head of the latter. In the actuator device, a uniform piezoelectric material layer is formed all over the entire surface of a vibration plate by a film forming technique, and then cut into pieces each with a shape corresponding to each pressure generating chamber by a lithography method. In this way, piezoelectric elements are formed independently for each pressure generating chamber.
Lead zirconate titanate (PZT) is an example of a material for the piezoelectric material layer constituting the piezoelectric element. In this case, when the piezoelectric material layer is baked, the lead component of the piezoelectric material layer is diffused into a silicon oxide (SiO2) film which is formed on the surface of the passage-forming substrate made of silicon (Si), and which constitutes the vibration plate. The lead component thus diffused lowers the melting point of the silicon oxide, so that the silicon oxide film is melt by the heat generated when the piezoelectric material layer is baked. For the purpose of solving such a problem, some piezoelectric actuator devices are provided with a zirconium oxide (ZrO2) layer formed on the silicon oxide film to form a part of the vibration plate, and the zirconium oxide layer thus formed blocks the diffusion of the lead component of the piezoelectric material layer into the silicon oxide film (see, for example, JP-A-11-204849, esp. FIG. 1, FIG. 2, and page 5).
The actuator device with the above-described structure has a problem. The adhesion between the zirconium oxide layer and a lower electrode layer formed on top of the zirconium oxide layer as well as between zirconium oxide layer and a silicon oxide film that lies under the zirconium oxide layer is not sufficiently strong. As a consequence, when the actuator device is driven to produce flexure vibration, a delamination may occur between the lower electrode and the zirconium oxide layer, and between the underlying film and the zirconium oxide layer. This kind of problem occurs not only in the actuator device mounted on a liquid-jet head, such as an ink-jet recording head, but also in actuator devices mounted on other apparatuses.